The present invention relates to an actuator for a transfer stage for performing a wide range of transfer motion with submicron accuracy at high speed.
A conventional method for driving a stage in combination with a piezo electric device is described in Japanese Patent Application Laid-Open No. 62-58883.
An example of this conventional actuator is shown in FIG. 2. In the conventional actuator, a drive head 3 is always pressed against a driven body 4 by an elastic body 7.
To piezo electric devices 1 and 2, a sine wave voltage which matches with the resonance frequency that is a function of the stiffness of the piezo electric devices is applied from a power source connected to the piezo electric devices 1 and 2. In this case, the phases of the voltages applied to the piezo electric devices 1 and 2 are shifted by 90.degree.. By doing this, since the piezo electric devices 1 and 2 move independently, the drive head 3 which is in contact with the two piezo electric devices traces an elliptical orbit. By setting the elastic force of the above elastic body so that the resonance frequency determined by the elastic force of the elastic body 7 matches with the frequency applied to the above piezo electric devices, the driven body 4 can be moved in one direction by the drive head 3 tracing the above elliptical orbit. By setting the above phase difference to -90.degree., the rotational direction of the above elliptical orbit can be reversed and the movement direction can be reversed.
However, since the above conventional method uses the resonance of the piezo electric devices, the speed with which the body 4 can be driven is limited to the intrinsic frequency determined by the stiffness of the above pair of piezo electric devices. Furthermore, since the method uses a stationary wave for driving, it is difficult to perform fine adjustment such as transfer at different voltage periods. The conventional method cannot be used as a fine transfer mechanism due to these restrictions and it is thus necessary to install a fine transfer mechanism separately.